sighs Okay, I'm gonna be blunt here. When you start the Supporter Program, no matter how amazing your rewards are (and some people do get very creative with theirs), you're not going to be making hundreds of dollars right off the bat. There are comics on Tapastic with -thousands- of readers but maybe just barely making $100 through the Support Program. I've had the Support Program set up for a couple months now and I consider myself lucky that I'm already at $19/month.
With the rewards I have set up, I have it so that you need to accumulate $200 in supporter money to get a cameo; there are other comics that have this range as well for cameos. Will anyone ever get to that? Maybe (I have a friend who's working towards it) but with a rate of only $19 a month (with many of my supporters giving $1/month, which is the standard), it'll probably be a looong time, unless someone is feeling super generous (which would be awesome, but the chances are slim).
And yes, there are people like GamerCat that are making somewhere around $600/month, but this was after they spent years branding themselves and making themselves recognizable.
You have Heart of Keol, which is -awesome- because that series is growing in popularity. But the problem you're worried about having might not be a problem at all, and expecting to have people clawing for rewards when your comic is still young is a pipe dream at best, and over-expecting at its worst (I'm sorry if that sounds mean, it's just the harsh reality of it).
All I can say is, if that's really a big problem for you, set the bar high for that reward. Make them work for it, ya?